H1B Visa Lottery is nothing but randomly choosing the required H1B visa petitions from received set of H1B visa applications by computer generated algorithm.
Why does USCIS conduct lottery ?
USCIS conducts lottery to give fair chance to everyone applied to H1B petition on the same day, as they cannot time stamp petitions received on a particular day.
What are the scenarios for H1B lottery ?
H1B lottery typically occurs only when USCIS receives more number of petitions than the required number to reach H1B cap. There can be two cases. In case 1, like in FY 2009, when there was too much demand on day 1 of H1B season , they would put all the petitions received in a pile and pick randomly using computer generated algorithm required to meet the cap ( 65,000 for regular quota). In case 2, when the H1B cap was not reached on first few weeks or days and there are more petitions received in the last day …for instance, if USCIS needs only 1000 to reach cap, but they received 1500 petitions on that last day, then USCIS would use Lottery to pick the 1000 petitions.